This invention relates generally to a miniature motor used for audio equipment, precision equipment, automotive electrical equipment, etc., and more specifically to improvements of means for fixedly fitting input terminals to a case cap comprising a miniature motor.
FIG. 1 is a longitudinal sectional view illustrating a miniature motor of a conventional type. In FIG. 1, reference numeral 1 refers to a case made of a metallic material, such as mild steel, formed into a bottomed hollow cylindrical shape and having an arc-segment-shaped permanent magnet 2 fixedly fitted on the inner circumferential surface thereof. In the case 1 disposed is a rotor 5 comprising an armature 3 facing the permanent magnet 2, and a commutator 4. Next, numeral 6 refers to a case cap made of an insulating material, such as a resin material, fitted to an open end of the case 1. Numeral 7 refers to a brush provided in such a manner that the free end thereof makes sliding contact with the commutator 4, and disposed on the case cap 6, together with an input terminal 8 electrically connected to the brush 7. Numerals 9 and 10 denote bearings, each fixedly fitted to the bottom of the case 1 and the central part of the case cap 6, respectively, to rotatably support shafts 11 and 12 constituting the rotor 5.
With the above construction, when current is fed from the terminals 8 to the armature 3 via the brushes 7 and the commutator 4 comprising the rotor 5, rotating force is imparted to the armature 3 existing in a magnetic field formed by the permanent magnet 2 fixedly fitted to the inner circumferential surface of the case 1, causing the rotor 5 to rotate, driving external equipment (not shown) via the shaft 11 on the output side.
Conventional means for fixedly fitting the input terminals 8 to the case cap 6 in the miniature motor having the aforementioned construction include that shown in FIG. 2. That is, a serrated projection 13 is provided on the side edge of the input terminal 8, and press-fitted into a hole 14 provided on the case cap 6. In this case, the width W.sub.1 of the hole 14 is made slightly smaller than the width W.sub.2 of the serrated projection 13 on the input terminal 8. Thus, as the input terminal 8 is press-fitted from under into the hole 14, the projection 13 proceeds in the hole 14 while deforming or shaving off the side edge of the hole 14, holding the input terminal 8 securely in position.
With the above construction, even when external force P is exerted to the input terminal 8 in the direction shown by an arrow in the figure, the input terminal 8 and the brush 7 connected thereto or formed integrally therewith can be held in place. The input terminal 8, however, which is held in place by frictional force alone between the projection 13 and the hole 14, has small resistance to the external force P. Furthermore, when the input terminal 8 is press-fitted into the hole 14, the projection 13 proceeds in the hole 14 while shaving off the side edge of the hole 14, as noted earlier. This causes the input terminal 8 to be deformed, or causes chips to adhere on the inside surface of the case cap 6 or on the surfaces of the input terminal 8, the brush 7, etc., causing adverse effects on the characteristics of the motor.
Next, FIGS. 3 is a cross-sectional front view, illustrating another example of conventional means for fixedly fitting the input terminal 8 to the case cap 6, and FIG. 4 is a longitudinal sectional view illustrating an area in the vicinity of the input terminal 8. Like parts are indicated by like reference numerals shown in FIG. 2. In FIGS. 3 and 4, numeral 15 refers to a lanced and raised piece provided in advance in the central part of the input terminal 8. The size t.sub.1, in the thickness direction of the hole 14 provided on the case cap 6, is made smaller than the size t.sub.2 in the thickness direction of the lanced and raised piece 15. Thus, the input terminal 8 can be locked to a predetermined location, as in the case of FIG. 2, by press-fitting the input terminal 8 from under into the hole 14.
The embodiment having the aforementioned construction has a better engaging and locking action than the embodiment shown in FIG. 2, due to the resiliency of the lanced and raised piece 15. But the strength to withstand the external force P in the direction shown by an arrow is small because the fixedly fitting force relies solely on the frictional force between the lanced and raised piece 15 and the hole 14. In addition, there is a fear that chips are generated when the input terminal 8 is press-fitted to the hole 14.
FIG. 5 is a longitudinal sectional view illustrating still another embodiment of conventional means for fixedly fitting the input terminal 8 to the case cap 6. Like parts are indicated by like numerals used in FIG. 4. In FIG. 5, t designates a thickness of the input terminal 8. In the embodiment shown in FIG. 5, the lanced and raised piece 15 is formed in such a manner as to appear on the outer end face of the case cap 6 by the resiliency of the lanced and raised piece 15 when the input terminal 8 is press-fitted into the hole 14. This allows the lanced and raised piece 15 to act as a retaining stopper to withstand the external force P in the direction shown by the arrow.
There still remains a problem that chips are generated, as in the case of the embodiment shown in FIG. 4, because the lanced and raised piece 15 proceeds while shaving off the inside surface of the hole 14 when the input terminal 8 is press-fitted into the hole 14. In addition, there is a likelihood of the size t.sub.3 of the hole 14 in the thickness direction becoming larger than the thickness t of the input terminal 8, thus reducing the engaging and locking action caused by frictional force. Furthermore, there often occur unwanted phenomena including a gap C being formed between the free end of the lanced and raised piece 15 and the outer end face of the case cap 6, or of the free end of the lanced and raised piece 15 not being exposed completely on the outer end face of the case cap 6. This also poses a problem that the lanced and raised piece 15 cannot have a stopper action as expected.
To overcome the aforementioned problems, the present Applicant has filed an application for an invention of a miniature motor comprising a case made of a metallic material, formed into a bottomed hollow cylindrical shape, and having a permanent magnet fixedly fitted to the inner circumferential surface thereof, a rotor comprising an armature, which faces the permanent magnet, and a commutator, and a case cap having brushes making sliding contact with the commutator, and input terminals electrically connected to the brushes; the rotor being rotatably supported by bearings provided on the bottom of the case and the case cap; characterized in that the input terminals are press-fitted to the case cap made of a resin material, and then fixedly fitted to the case cap via lanced and raised pieces formed on the input terminals at locations near the outer end face of the case cap. (Refer to U.S. patent application Ser. No. 07/918,565, now U.S. Pat. No. 5,270,599.)
FIG. 6 is a partially cross-sectional front view illustrating a case cap in an embodiment of the aforementioned improvement invention. FIG. 7 is a diagram illustrating the essential part viewed from the direction shown by arrow A in FIG. 6. Like parts are indicated by like numerals shown in FIGS. 3 through 5. In FIGS. 6 and 7, numeral 15 refers to a lanced and raised piece. The lanced and raised piece 15 is formed on an input terminal 8 so that the free end 15a of the lanced and raised piece 15 positively comes in contact with the outer end face 6a of the case cap 6, by a means as will be described later, after the input terminal 8 has been press-fitted into the hole 14 and secured or fitted to a predetermined location. The cross-sectional internal dimensions of the hole 14 provided on the case cap 6 is made essentially the same as the cross-sectional external dimensions of the input terminal 8.
With the aforementioned construction, since the input terminal 8 comes in close contact with the hole 14 provided on the case cap 6, and the free end 15a of the lanced and raised piece 15 positively comes in contact with the outer end face 6a of the case cap 6, the free end 15a acts as a stopper, increasing the retaining effect, even if external force P is exerted in the direction shown by the arrow. When the input terminal 8 is press-fitted into the hole 14, no chips are generated even when the external dimensions of the input terminal 8 is made essentially the same as the internal dimensions of the hole 14, because the lanced and raised piece 15 has not yet been formed on the input terminal 8. Thus, the surface and surrounding area of the input terminals 8 and the brushes 7 can be kept clean.
FIG. 8 is a diagram of assistance in explaining the construction of an input terminal fitting jig in an embodiment of the aforementioned improvement invention. In FIG. 8, numeral 21 refers to a table having a holder 22 at the central part thereof, and a receiving blade 23 at a location corresponding to the location to which the input terminal 8 of the case cap 6 is fitted. Numeral 24 refers to a lancing and raising blade provided in such a manner that the lancing and raising blade 24 can be engaged with or disengaged from the receiving blade 23, and moved horizontally on the table 21 by a driving member 25. Numeral 26 refers to rollers rotatably provided at the rear ends of the driving member 25 having the lancing and raising blade 24.
Next, numeral 27 refers to a working member formed in a vertically movable manner via a guide (not shown) provided on the table 21; with a press-fitting member 28 provided at the central part thereof in such a manner as to be vertically movable with the working member 27, and roller retainers 29, which can be engaged with or disengaged from the rollers 26, provided on the outer end thereof. Numeral 30 refers to a cylinder connecting shank, and 31 to a spring; each provided in such a manner as to drive the working member 27 and the press-fitting member 28.
FIG. 9 is an enlarged perspective view illustrating the receiving blade 23 and the lancing and raising blade 24 shown in FIG. 8. Like parts are indicated by like numerals shown in FIG. 8. In FIG. 9, numeral 23a refers to a blade formed by cutting the upper end of the receiving blade 23 into a square or U shape in such a manner as to engage with the lancing and raising blade 23 protruded in a triangular shape in longitudinal section. The receiving blade 23 and the lancing and raising blade 24 should preferably be formed using a jig material, such as tool steel. The upper end surfaces of the receiving blade 23 and the lancing and raising blade 24 are formed in such a manner as to be flush with the upper end surface of the holder 22, that is, the outer end surface of the case cap 6.
With the above construction, a case cap 6 is placed and positioned on the holder 22, as shown in FIG. 8, with the inside side surface upward. The input terminal 8 (in the state where the brush 7 is bonded thereto, as shown in FIGS. 3 and 4, and the lanced and raised piece 15 has not yet been formed) is inserted, and the working member 27 and the press-fitting member 28 are lowered. The input terminal 8 is press-fitted into the case cap 6 by the press-fitting member 28. As the working member 27 is lowered while the press-fitting member 28 is kept pushed slightly onto the case cap 6, the roller retainers 29 are engaged with the rollers 26, causing the driving member 25 to move to the side of the input terminal 8. Thus, the lancing and raising blade 24 proceeds and cuts into the input terminal 8, and engages with the receiving blade 23 to form the lanced and raised piece 15, as shown in FIGS. 6 and 7. As a result, the input terminal 8 is engaged with and fitted to the case cap 6. Upon completion of the engaging and fitting operation, the component members are operated in a reversed direction (opposite the direction shown by the arrow in FIG. 8) to remove the case cap 6. Then, a new case cap is loaded to repeat the above operations.
With the aforementioned construction, the free end of the lanced and raised piece 15 provided on the input terminal 8 can be accurately made flush with the outer end surface of the case cap 6. Thus, the input terminal 8 can be positively engaged with and fixedly fitted to the case cap 6 without relative movement caused between the input terminal 8 and the case cap 6 even when external force is applied.
In miniature motors used for automotive electrical components, however, connectors are frequently used to feed power to the input terminal 8. In this type of miniature motor, a hollow tubular connecting member (not shown) is provided integrally with the case cap 6 in the vicinity of the free end of the input terminal 8. Thus, this arrangement makes it impossible to put this invention into practical use because the aforementioned connecting member may interfere with the input terminal 8 when forming the lanced and raised piece 15 on the input terminal 8 after the input terminal 8 has been press-fitted, as shown in FIGS. 8 and 9. For this reason, the conventional means for fixedly fitting the input terminals has to be relied upon. Thus, a number of problems are encountered, such as the generation of chips, or lowered reliability due to insufficient fixing strength.
Since the strength for fixedly fitting the input terminals 8 to the case cap 6 relies solely on the frictional force between both, a larger resistance to external pulling force is required for a type using connectors, for example, while a sufficient resistance to external pulling force is provided for types of ordinary specifications.